1. Field of the Invention
The present invention generally relates to an adapter for interconnecting at least one of a plurality of types of blasting caps and primers so as to provide delayed ignition of the primers while utilizing a single detonating cord within a blast hole to accomplish the multiple ignitions. More particularly, the invention relates to an arrangement that provides for a shock tube element as a component for attaching a primer to an adapter.
2. Description of the Prior Art
Modern mining, quarrying and construction excavation requires the use of explosives in such large quantities in single bore holes as to cause annoying vibration to people and actual damage to structures. To prevent this annoyance and damage, and to comply with Federal Regulations, a single explosive charge must sometimes be divided into two or more charges detonated at substantially different instants of time, each charge in a bore hole being separated from next-in-line charges by inert material, usually small sized rock particles. The appropriate delay times between the segmented charges is a matter of debate and choice, and in general these delays are between 8 and 25 milliseconds. As such, in an extreme but realistic situation wherein there may be eight individual explosive charges in a single bore hole (these charges being commonly referred to as decks or deck charges), there may be a total elapsed time from the first deck detonation to the last detonation of 175 milliseconds. Until recently, the only practical way to achieve an in-hole delay was to use individually delayed electric or non-electric blasting caps in a suitable primer, the primer being appropriately imbedded in or in contact with the explosive of each deck.
All explosives used today for surface mining are insensitive compared to previously used nitroglycerin explosives, such as dynamite Insensitive explosives will not detonate from an impact of a hard object, such as a steel shovel bucket, whereas nitroglycerin explosives will so detonate. These less sensitive explosives are commonly referred to as blasting agents, such blasting agents being generally understood to be any explosive mixture which cannot be detonated unconfined by a number 8 test cap. Most of the insensitive explosives utilize ammonium nitrate as the principal explosive ingredient. In dry form, the ammonium nitrate is generally mixed with 5% to 6% of fuel oil and is commonly referred to as ANFO. Additionally, there are methods of combining the ammonium nitrate with water and other ingredients to produce a waterproof explosive. Inasmuch as ANFO is not waterproof, the waterproof mixes per se are referred to as slurries or emulsions, depending on the ingredients used and the manufacturer's pleasure. Sensitivity of explosives currently in use range from dynamites to blasting agents, dynamites being readily initiated by detonating cords or caps and blasting agents generally requiring a primer which is initiated by a cord or cap.
In effect, almost none of the currently used explosives can be detonated by a blasting cap and as such, these explosives when used in surface blasting must be detonated by a primer. A primer is generally understood to be a package of explosive into which has been inserted a cap or to which has been attached a detonating cord. The cap or cord then detonates the primer, and the primer in its turn detonates the explosive with which it is in contact.
Primers can be packages of dynamite, cast primers or slurry primers. Dynamite primers are not generally used in holes having diameters of six inches or more, while it is commonly used in four inch and smaller holes. Cast primers are made from different mixtures of pentalite, which is a generic term referring to the ingredients which can vary in composition. However, at ordinary temperatures, pentalite is a solid, very insensitive explosive which is quite powerful when detonated. Slurry primers are simply a more sensitive composition of slurries contained in either a flexible or near rigid container.
All rigid or semi-rigid primers, such as cast primers or slurry primers, contained within a shell of hard or stiff plastic, as opposed to a flexible plastic film, have preformed holes within the body of the primer per se and shell to accept detonating cords or caps, or both. As above mentioned, cast primers and slurry primers are caused to detonate either by a blasting cap or a detonating cord, and the blasting caps may be of either an electric or non-electric actuated construction. Electric blasting caps are manufactured by several companies and have the same general appearance and operating characteristics. Non-electric blasting caps are made by several different companies, but they are not similar in operating principle. However, all caps are themselves similar in appearance, i.e., a rigid metal shell which can be inserted into a receptacle called a cap well contained within the primer.
In addition to a cap well, primers always have a hole or cord tunnel parallel to the axis of the primer, and generally coinciding with the axis, through which detonating cord may be passed. Alternatively, a primer may be provided with two cord tunnels passing completely through the primer, as opposed to a cord tunnel and a cap well. If the primer is to be initiated by a detonating cord, the cord or cords are passed through the tunnel or tunnels, with the primers per se being threaded into the cord(s). If a cap is used, the cap is inserted into the cap well, the lead to the cap having been first passed through the tunnel, or, in the case of certain kinds of non-electric caps, the lead may be taped to the outside of the primer.
Detonating cord has a burn velocity of 18,000 to 22,000 feet per second, so when more than one primer is threaded onto the same piece of detonating cord, as they would be in a single blast hole, all of the primers detonate at essentially the same instant. For example, a blast hole 100 feet deep with six primers 12 feet apart located from the bottom of the hole upwardly, would see the top primer detonated first while the bottom primer being located 72 feet below it would detonate 0.0036 seconds later.
The advantage of blasting caps is that different delays can be used in these multiple primer arrangements. The disadvantage is that each cap must have a separate lead, meaning that for six delays, there would be six electric blasting cap wires coming out of the hole, or in the case of non-electric delays, six different non-electric leads.
Certain cast primer manufacturers have designed primers which house specially arranged delay cap assemblies. The primers can be threaded onto a detonating cord and allowed to slide down the cord as desired, eventually coming to rest in a blast hole at a predetermined depth. When the cord detonates, it activates the delay cap, which in turn detonates the primer after a predetermined delay. Thus, there only needs to be one cord coming out of the hole and it can accommodate any number of delay primers. In this respect, at least two of the manufacturers are the Austin Powder Company and the Atlas Powder Company. The delay primers manufactured by both of these companies incorporate specific proprietary delays which cannot and are not used in any other way for any other purpose. The use of either requires two parts, i.e., the primer which is designed for the cap and the cap which is designed for the primer. These specially designed primers and caps are not interchangeable, nor can any part be used for any other purpose independently therefrom.
Several patents describing assemblies of delay caps with primers (the term "primer" as used hereinafter refers to any primer other than dynamite) are: U.S. Pat. Nos. 3,590,739, 3,125,024, 3,987,733, 4,023,494, 4,037,536, 4,060,033, 4,165,691, 4,178,852, and 4,141,296. These patents showing a specific primer body and a specific delay cap element whereby each primer body and cap element is used solely with each other, whether taken and viewed throughout singly or in combination with each other, are believed to have no bearing on the patentability of any claim of the invention.
As such, there can be seen to exist a need for a means of joining any type and design of primer to any type and design of blasting cap. In this respect, the present invention substantially fulfills this need.
Effectively, the present invention provides means of assembling in the field and at the point of use commonly used and everywhere available non-electric delay caps, such as the HD Nonel Primadet and the Primaline Primadet (both manufactured by the Ensign Bickford Company, of Simsbury, Conn.) and any primer containing a cap well and cord tunnel, such primers being made by several companies including, but not limited to, the Trojan Powder Co., Ireco Chemicals Co., Gulf Chemicals Division, Austin Powder Co., and Sierra Chemicals Co. Specifically, until the presentation of the present invention, there has been no way to join primers made by any one of these companies to any non-electric delay cap, so as to permit detonation in multiple, delayed units in a single bore hole from a single line of detonating cord. Therefore, to achieve multiple delays in a single bore hole with any of these standard primers has always required separate leads to each cap, regardless of whether the cap is of an electric or non-electric construction.